Edit Polylines (.NET)

2D and 3D polylines, rectangles, polygons, donuts, and 3D polygon meshes are all polyline variants and are edited in the same way.

AutoCAD recognizes both fit polylines and spline-fit polylines. A spline-fit polyline uses a curve fit, similar to a B-spline. There are two kinds of spline-fit polylines: quadratic and cubic. Both polylines are controlled by the SPLINETYPE system variable. A fit polyline uses standard curves for curve fit and utilizes any tangent directions set on any given vertex.

To edit a polyline, use the properties and methods of the Polyline, Polyline2d, or Polyline3d object. Use the following properties and methods to open or close a polyline, change the coordinates of a polyline vertex, or add a vertex:

Closed property

Opens or closes the polyline.

ConstantWidth property

Sets the constant width for a lightweight and 2D polyline.

AppendVertex method

Adds a vertex to a 2D or 3D polyline.

AddVertexAt method

Adds a vertex to a lightweight polyline.

ReverseCurve

Reverses the direction of the polyline.

Use the following methods to update the bulge or width of a polyline:

SetBulgeAt

Sets the bulge of a light polyline, given the segment index.

SetStartWidthAt

Sets the start width of a lightweight polyline, given the segment index.

Straighten

Straightens a 2D or 3D polyline.

Edit a polyline

This example creates a lightweight polyline. It then adds a bulge to the third segment of the polyline, appends a vertex to the polyline, changes the width of the last segment, and finally closes the polyline.

C# Example

using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;
 
[CommandMethod("EditPolyline")]
public static void EditPolyline()
{
    // Get the current document and database
    Document acDoc = Application.DocumentManager.MdiActiveDocument;
    Database acCurDb = acDoc.Database;

    // Start a transaction
    using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
    {
        // Open the Block table for read
        BlockTable acBlkTbl;
        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId,
                                     OpenMode.ForRead) as BlockTable;

        // Open the Block table record Model space for write
        BlockTableRecord acBlkTblRec;
        acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace],
                                        OpenMode.ForWrite) as BlockTableRecord;

        // Create a lightweight polyline
        using (Polyline acPoly = new Polyline())
        {
            acPoly.AddVertexAt(0, new Point2d(1, 1), 0, 0, 0);
            acPoly.AddVertexAt(1, new Point2d(1, 2), 0, 0, 0);
            acPoly.AddVertexAt(2, new Point2d(2, 2), 0, 0, 0);
            acPoly.AddVertexAt(3, new Point2d(3, 2), 0, 0, 0);
            acPoly.AddVertexAt(4, new Point2d(4, 4), 0, 0, 0);

            // Add the new object to the block table record and the transaction
            acBlkTblRec.AppendEntity(acPoly);
            acTrans.AddNewlyCreatedDBObject(acPoly, true);

            // Sets the bulge at index 3
            acPoly.SetBulgeAt(3, -0.5);

            // Add a new vertex
            acPoly.AddVertexAt(5, new Point2d(4, 1), 0, 0, 0);

            // Sets the start and end width at index 4
            acPoly.SetStartWidthAt(4, 0.1);
            acPoly.SetEndWidthAt(4, 0.5);

            // Close the polyline
            acPoly.Closed = true;
        }

        // Save the new objects to the database
        acTrans.Commit();
    }
}